Activation kinetic model and mechanisms for alkali-activated slag cements

Abstract

A new model for reaction kinetics of waterglass-activated slag cements based on calorimetry results has been proposed. The model is based on solid-state kinetic models for single-particle kinetics. It accounts for the different mechanisms during alkali-activation of slag with waterglass considering successive application of single-particle models. The process of alkali-activation of slag with waterglass typically consists of two accelerated periods, separated by an induction period. The first accelerated period is described by the succession of a nucleation and growth process and a contraction volume process and the second accelerated period is described by the succession of a nucleation and growth process, a contraction volume process and a diffusion process. The induction period is described by zero-order kinetics signifying that the dissolution of slag does not stop during this period. The model has been tested against both newly measured experimental data and a comprehensive dataset extracted from the literature to cover wide ranges of slag composition and waterglass solutions. The model is found to successfully describe a wide range of experimental data with R2 values greater than 0.95 for all datasets. In addition, detailed justification is provided on the choice of the mechanisms proposed in the model together with different hypotheses laid in literature and observations made on microstructure development. Finally, correlations between mix characteristics and parameters of the model are proposed. Interpretations of these correlations seem to be pertinent with experimental observations such as the importance of the pH of the solution on the kinetics, the role of silicon ions as nucleation sites and low apparent activation energies for the diffusion governing step.